1. Field of the Invention
The present invention relates to a magnetic head positioning mechanism for a magnetic disk device, and more particularly to a magnetic head positioning mechanism capable of positioning of a magnetic head in the magnetic disk device which is used as a peripheral or terminal device in an electronic computer system or the like.
2. Description of the Prior Art
The rapid advancement of the computer technology makes rapid development of the magnetic disk devices, which are internal or external memory devices of the peripheral or terminal devices of the computer. In the magnetic disk device, with increasing capability of high density data recording of the storage medium, the magnetic head positioning mechanism is required to more precisely position the magnetic head in place.
One example of the conventional magnetic head positioning mechanism, is "a positioning mechanism of magnetic disk device" which is disclosed in Japanese Laid-Open No. 61-82386. This prior art will be described with reference to FIG. 1 which shows a cross-section of the magnetic head positioning mechanism, FIG. 2 which shows a side view of the mechanism in FIG. 2 when the pivot shaft thereof is used in horizontal position, and FIG. 3 which shows a right side view of FIG. 1. The magnetic head positioning mechanism generally comprises a housing 1 having at least two plates opposing each other, and a pivot mechanism 2 supported between the plates of the housing 1. The pivot mechanism 2 comprises a carriage 3 which is supported by means of a pivot shaft 4 and bearings 5 to swing about a longitudinal axis of the pivot shaft 4, a plurality of head-arms 6 which are fixed at base ends thereof to one side of the carriage 3, a plurality of magnetic heads 7 which are attached to opposite tip ends of the head-arms 6, a coil 8 which is arranged on the opposite side of the carriage 3. A pair of magnetic circuits are secured within the housing 1, 1, each circuit facing the turns of the coil 8. The magnetic circuits 9, 9 and the coil 8 constitute a voice-coil motor 10 which drives the mechanism 2. Further, numeral 11 denotes a bracket for supporting one of the magnetic circuits 9.
The operation of the magnetic head positioning mechanism having the above-mentioned structure will be described hereinafter. The coil 8 produces a repulsive force against the magnetic circuit 9, 9 when a driving current is supplied to the coil 8 of the voice-coil motor 10, and the pivot mechanism 2 swings about the pivot shaft 4.
Concerning the magnetic head positioning mechanism which operates as mentioned above, a controlling circuit (not shown) determines an amount of angle by which the pivot mechanism 2 pivots on the basis of processing data for positioning the magnetic head, and performs positioning of the magnetic head 7. Generally, the magnetic head positioning mechanism comprises the carriage 3 and the head-arms 6 which are made from the same material. Light and highly rigid metal materials such as aluminum (Al) and magnesium (Mg) have been used. The coil 8 is made from a copper (Cu) wire or an aluminum wire (Al). In the pivot mechanism 2 which is made from such materials, a distance L1 from the center of the pivot shaft 4 to the tip ends of the head-arms 6 is much longer than a distance L2 from the center of the pivot shaft 4 to the end surface of the coil 8, therefore the center of gravity of the pivot mechanism 2 is not on the pivotal axis of the mechanism 2 but at somewhere on the head-arms 6.
Since a conventional magnetic head positioning mechanism is constituted as described hereinbefore, the driving force required for driving the mechanism is independent of its pivotal direction if the magnetic head positioning mechanism is arranged in such a way that the head arms 6 pivot on a vertical axis as shown in FIG. 1. On the contrary, if the magnetic head positioning mechanism is arranged in such a way that the head arms 6 pivot about a horizontal axis as shown in FIG. 2, since the rotational center is not coincident with the center of gravity of the pivot mechanism 2, the gravitational force acting on the head arms is larger than that acting on the coil 8. Accordingly, the driving force required in the direction a is smaller than that in the direction b, therefore it is difficult to control the magnetic head positioning mechanism with good stability.